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BIOL243 > theme 4c > Flashcards

theme 4c Flashcards

1
Q

what is gene flow?

A

the movement of alleles and genotype into and out of a population (migration).

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2
Q

what effect does gene flow have on populations?

A

can introduce new alleles into population and change the genotype and allele frequencies from that predicted for HWE

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3
Q

what determines the significance of the impact of gene flow?

A

how different the gene pool within the population is compared to the populations from which the individuals migrated

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4
Q

what is genetic drift?

A

change in allele frequencies simply due to chance

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5
Q

what effect does genetic drift have on populations?

A

causes allele frequencies to move up and down in unpredictable ways. can have a major impact

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6
Q

what is the founder effect?

A

(type of genetic drift). when a few individuals of a population colonize a different location and start a new population (but the original population remains)

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7
Q

what effect does the founder effect have on populations?

A

causes a reduced genetic variety in newly established population. chance changes in allele frequencies can change which alleles are more or less common compared to original population (which still exists)

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8
Q

what is a population bottleneck?

A

(type of genetic drift). when a large portion of the population is killed (the population size is greatly reduced)

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9
Q

what effect do bottlenecks have on population?

A

decreased gene pool size. chance changes in allele frequencies can change which alleles are more or less common compared to original population (which no longer exists) and some alleles can be lost forever

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10
Q

how do new alleles arise?

A

through mutation, which is random, spontaneous, and directionless

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11
Q

what are the 5 types of mutations?

A 
① point mutation
② insertion
③ deletion
④ inversion
⑤ duplication
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12
Q

what is a point mutation?

A

change of a single nucleotide base (can also be called substitution)

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13
Q

what is an insertion mutation?

A

one or more nucleotide bases are introduced into a DNA sequence

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14
Q

what is a deletion mutation?

A

one or more nucleotide bases are removed from a DNA sequence

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15
Q

what is an inversion mutation?

A

a segment of DNA breaks and is inserted back into its original position in the reverse orientation

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16
Q

what is a duplication mutation?

A

DNA is copied twice. duplication can be part of a gene, a whole gene, or an entire genome

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17
Q

what is directional selection?

A

natural selection where individuals near one end of the phenotypic spectrum have the highest relative fitness

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18
Q

what effect does directional selection have on the existing mean and variability?

A

shift a trait away from the original mean and towards a new mean.
variability may be decreased

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19
Q

what is stabilizing selection?

A

natural selection where intermediate phenotypes have the highest relative fitness

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20
Q

what effect does stabilizing selection have on the existing mean and variability?

A

no change in mean.

reduces genetic and phenotypic variation (less variability, alleles at extremes may be lost)

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21
Q

what is disruptive selection?

A

natural selection where extreme phenotypes have a higher relative fitness than intermediate ones

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22
Q

what effect does disruptive selection have on the existing mean and variability?

A

no change

increased variability.

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23
Q

what is inbreeding?

A

a type of non-random mating where mating occurs between individuals that are more closely related

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24
Q

what is the effect of inbreeding on allele and genotype frequencies?

A

inbreeding causes an increase in the proportion of homozygous individuals at both extremes, and a decrease in number of heterozygous, but does not change allele frequency at all

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25
Q

what is inbreeding depression?

A

the negative effect inbreeding often has on species (including humans)

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26
Q

what is the explanation for inbreeding depression?

A

many deleterious genes (genes that code for a non-functioning protein) are recessive and therefore are more impactful in communities where inbreeding causes the proportion of homozygous individuals to increase

27
Q

what is sexual selection?

A

selection by an individual where they consider a potential mate’s specific characteristics before mating with them

28
Q

what is intersexual selection?

A

selection based on interactions between males and females (selection as a result of (usually) females preferring mates with a particular characteristic)

29
Q

what is intrasexual selection?

A

selection based on interactions of individuals of the same sex (such as fights between males using ornaments such as horns or tusks)

30
Q

how can recessive genes selected against by natural selection persist in a population?

A

by being masked by dominant alleles in heterozygotes, where they will not be selected against

31
Q

what is balancing selection?

A

natural selection where more than one allele is actively preserved in a population

32
Q

what are 3 types of cases of balancing selection?

A

① heterozygote advantage
② different alleles favoured in different environments
③ when the rarity of a phenotype provides selective advantage

33
Q

what is assortative mating?

A

non-random mating where individuals with similar genotypes and/or phenotypes (but not necessarily familiar relatedness) mate with each other more frequently than would be expected under a random mating pattern

34
Q

what is the morphological species concept?

A

the idea that all individuals of a species share measurable traits that distinguish them from individuals of other species

35
Q

what are the pros and cons of the morphological species concept?

A

PROS:
- allows easiest possible recognition of species that have already been identified (practical, easy to use)
- can be applied to extinct organisms
CONS:
- individuals of one species can vary a lot in appearance, and individuals of different species can look extremely similar
- tells us very little about the evolutionary processes that produce new species

36
Q

what is the biological species concept?

A

defining biological species as groups of naturally interbreeding populations that are reproductively isolated from other such groups

37
Q

what are the pros and cons of the biological species concept?

A

PROS:
- easy to apply in principle (clear criteria)
- clear evolutionary justification
CONS:
- doesn’t apply to asexually reproducing organisms
- cannot be applied to extinct organisms because their reproductive habits cannot be observed

38
Q

what is the phylogenetic species concept?

A

the use of morphological and genetic sequence data to construct evolutionary trees for organisms and defining a phylogenetic species as a cluster of populations

39
Q

what are the pros and cons of the phylogenetic species concept?

A

PROS:
- can be applied to any species (including extinct and asexually reproducing species)
CONS:
- detailed evolutionary histories have not yet been described for many species, it is not yet possible to apply it to all species.

40
Q

what is a subspecies?

A

a grouping of a population within a species that is distinct genetically and/or phenotypically from other such groupings. also can be referred to as race

41
Q

what is a ring species?

A

species that have a ring-shaped geographical distribution that surrounds an uninhabitable terrain (this causes some species to be more distant and therefore distinct (and possibly unable to reproduce))

42
Q

what does clinal variation refer to?

A

species that are distributed over a large, environmentally diverse area, resulting in a cline

43
Q

what is a cline?

A

a smooth pattern of variation across a geographical gradient

44
Q

what are reproductive isolating mechanisms?

A

biological characteristics that prevent individuals of different species from mating and producing successful progeny

45
Q

what are the 2 types of reproductive isolating mechanisms?

A

➝　prezygotic: pre-mating mechanisms

➝　postzygotic: post-mating mechanisms

46
Q

what are the 5 prezygotic isolating mechanisms?

A

➝　ecological isolation: species live in different habitats
➝　temporal isolation: species breed at different times
➝　behavioural isolation: species cannot communicate
➝　mechanical isolation: species cannot physically mate
➝　gametic isolation: species have non-matching receptors on gametes

47
Q

what are the 3 postzygotic isolating mechanisms?

A

➝　hybrid inviability: hybrid offspring do not complete development
➝　hybrid sterility: hybrid offspring cannot produce gametes
➝　hybrid breakdown: hybrid offspring have reduced survival or fertility

48
Q

what is allopatric speciation?

A

(allo: different, patria: homeland)
speciation that takes place when a physical barrier divides a large population, or when a small population becomes separated from the main geographical distribution

49
Q

how does allopatric speciaton occur?

A

① two populations become geographically separate, preventing gene flow between them.
② the populations experience distinct mutations, different patterns of natural selection, and genetic drift, accumulating genetic differences that isolate them reproductively

50
Q

what is a secondary contact and what does it show?

A

a secondary contact is contact between two groups that have been geographically isolated after a long time. shows if the two populations have become reproductively isolated or not (if they’re developed into distinct species)

51
Q

what is species fusion?

A

when populations that did not become reproductively isolated after geographic isolation have a secondary contact and interbreed and then turn into one again.

52
Q

what are hybrid zones?

A

zones where two species going through allopatric speciation can produce viable hyrbids before they become totally reproductively isolated.

53
Q

what is reinforcement (when referring to reproductive isolation)?

A

when prezygotic isolation mechanisms evolve after postzygotic mechanisms have already been established

54
Q

what is sympatric speciation?

A

(sym: together, patria: homeland)

speciation that occurs between different subgroups within one population, not necessarily geographically isolated

55
Q

what is a host race (with respect to sympatric sepciation)?

A

the subpopulation that mutated and separated from the original population

56
Q

what are 3 genetic mechanisms of speciation?

A

① genetic divergence (allopatric)
② polyploidy (sympatric)
③ chromosome alterations (both)

57
Q

how does genetic diversion work in speciation?

A

when there is no gene flow between populations (allopatric speciation), the populations inevitably accumulate genetic differences through mutation, genetic drift, and natural selection.

58
Q

how does polyploidy work in speciation?

A

when ploidy changes, a separate species is produced because organisms with different ploidies cannot produce fertile offspring (if they can produce any at all) (therefore geographic separation is not necessary)

59
Q

what can cause polyploidy?

A

➝　autopolyploidy: chromosome duplication within a single species
➝　allopolyploidy: hybridization of different species

60
Q

what is an unreduced gamete?

A

gametes that (due to a spontaneous error in meiosis) receive the same number of chromosomes as a somatic cell

61
Q

how does speciation by genetic divergence compare to speciation by polyploidy?

A

speciation by polyploidy is much more rapid than by genetic divergence

62
Q

how does chromosome alteration work in speciation?

A

because chromosome rearrangements (such as due to inversions) inhibit chromosome pairing and recombination during meiosis, new genetic variations favoured by natural selection are conserved in rearranged segments, and so differences can accumulate and genetic divergence can occur at a faster rate than normal

63
Q

what is a vicariance event?

A

an event where a physical barrier (such as a new river) dives the geographic range of a population (and splits it into two separate populations with no gene flow between them)

64
Q

what is peripatric speciation?

A

allopatric speciation that occurs when the ancestral population “seeds” a small peripheral population, such as on an island. genetic divergence occurs over time, but most change occurs in the small population

BIOL243 (14 decks)

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